RESEARCH ON STABILITY OF SURROUNDING ROCK AND OPTIMAL DESIGN OF SUPPORTING MEASURES OF DEEPLY BURIED LONG TUNNELS

High external water pressure and high ground stress are common engineering problems in underground construction in water-rich areas in southwest China. This paper first analyzes the main geological engineering problems of the Jinping II Hydropower Station, followed by the analysis of the excavation methods and the tunnel stability based on the theory of elastic and plastic damage using FEM. An analytical method of the anchorage support and a 3-D nonlinear damage analysis method of the wall rock in the large derivation tunnels are proposed. Random distribution of the mechanical parameters is adopted in the analysis. A local sub-model is introduced to simulate the karst channel and to analyze the influence of external water pressure. The research of the optimal rock support design focuses on tunnel stability and penetrability. Finally, an estimation method for structural reinforcement requirement is suggested and a rock support design proposed.